How to use the stellar-base.Account function in stellar-base

constructor(response: ServerApi.AccountRecord) {
    this._baseAccount = new BaseAccount(response.account_id, response.sequence);
    // Extract response fields
    // TODO: do it in type-safe manner.
    forIn(response, (value, key) => {
      (this as any)[key] = value;
    });
  }

export function buildChallengeTx(
    serverKeypair: Keypair,
    clientAccountID: string,
    anchorName: string,
    timeout: number = 300,
    networkPassphrase?: string,
  ): string {
    const account = new Account(serverKeypair.publicKey(), "-1");
    const now = Math.floor(Date.now() / 1000);

    // A Base64 digit represents 6 bits, to generate a random 64 bytes
    // base64 string, we need 48 random bytes = (64 * 6)/8
    //
    // Each Base64 digit is in ASCII and each ASCII characters when
    // turned into binary represents 8 bits = 1 bytes.
    const value = randomBytes(48).toString("base64");

    const transaction = new TransactionBuilder(account, {
      fee: BASE_FEE,
      networkPassphrase,
      timebounds: {
        minTime: now,
        maxTime: now + timeout,
      },