<Query Kind="Program">
  <Reference>&lt;RuntimeDirectory&gt;\System.DirectoryServices.dll</Reference>
  <Reference>&lt;RuntimeDirectory&gt;\System.Configuration.dll</Reference>
  <Namespace>System.DirectoryServices</Namespace>
</Query>

void Main()
{
	List<UserDetailsViewModel> value = GetUserDetailsByGroupPath("LDAP://DC=acctprov,DC=loc", "a");

	value.Count().Dump();
}

public static List<UserDetailsViewModel> GetUserDetailsByGroupPath(string path, string lastNameLetterFilter = null)
{
	List<UserDetailsViewModel> results = new List<UserDetailsViewModel>();

	using (var entry = new DirectoryEntry(path))
	{
		var searcher = new DirectorySearcher(entry)
		{
			Filter = string.Format("(&(objectCategory=person)(objectClass=user)(memberOf=*)(sn={0}*))", lastNameLetterFilter ?? "")
		};

		searcher.PropertiesToLoad.Add("objectguid");
		searcher.PropertiesToLoad.Add("displayname");
		searcher.PropertiesToLoad.Add("givenname");
		searcher.PropertiesToLoad.Add("sn");
		searcher.PageSize = 250;

		using (var searchResults = searcher.FindAll())
		{
			foreach (SearchResult user in searchResults)
			{
				UserDetailsViewModel uvm = new UserDetailsViewModel();
				uvm.Uid = new Guid((byte[]) user.Properties["objectguid"][0]).ToString();
				uvm.DisplayName = user.Properties["displayname"][0].ToString();
				uvm.FirstName = user.Properties["givenname"][0].ToString();
				//broken uvm.MiddleName = user.Properties["middlename"][0].ToString();
				uvm.LastName = user.Properties["sn"][0].ToString();

				results.Add(uvm);
			}
		}
	}

	return results.OrderBy(x => x.LastName).ToList();
}

public class UserDetailsViewModel
{
	public string Uid {get;set;}

	public string DisplayName {get;set;}

	public string FirstName {get;set;}

	public string MiddleName {get;set;}

	public string LastName {get;set;}
}